Preparation of Laser Cladding Coating Undercooling Cu-based Alloy and Co on Non-equilibrium Solidification Structure

The effect of the gradient content of Co element on the solidification process of Cu-based alloy under deep under cooling conditions was explored.The non-equilibrium solidification structure of the under cooled alloy samples were analyzed.It is found that the rapidly solidified alloy has undergone twice grain refinement during the undercooling process.Characterization and significance of the maximum undercooling refinement structure of Cu60Ni35Co5 at T=253 K were analyzed.High-density defects were observed,such as dislocations,stacking faults networks,and twinning structures.The standard FCC diffraction pattern represents that it is still a single-phase structure.Based on the metallographic diagram,EBSD and TEM data analysis,it is illustrated that the occurrence of grain refinement under high undercooling is due to stress induced recrystallization.In addition,the laser cladding technology is used to coat Co-based alloy(Stellite12) coating on 304 stainless steel substrate;the microstructure of the coating cross-section was analyzed.It was found that the microstructure of the cross-section is presented as columnar crystals,planar crystals,and disordered growth direction,so that the coating has better hardness and wear resistance.By electrochemical corrosion of the substrate and coating,it can be seen that the Co and Cr elements present in the coating are more likely to form a dense passivation film,which improved the corrosion resistance of the coating.

Microstructure and Properties of AlCoCrFeNiTi High-Entropy Alloy Coatings Prepared by Laser Cladding

21-4N(5Cr21Mn9Ni4N)is extensively employed in the production of engine valves,operating under severe conditions.Apart from withstanding high-temperature gas corrosion,it must also endure the impact of cylinder explosion pressure.The predominant failure mode of 21-4N valves is abrasive wear.Surface coatings serve as an effective approach to prevent such failures.In this investigation,Laser cladding technology was utilized to fabricate AlCoCrFeNiTi high entropy alloy coatings onto the surfaces of 21-4N valves.According to the findings,the cladding zone has a normal dendritic microstructure,a good substrate-to-cladding layer interaction,and no obvious flaws.In terms of hardness,the cladding demonstrates an average hardness of 620 HV.The hardness has increased by 140%compared to the substrate.The average hardness of the cladding remains at approximately 520 HV even at elevated temperatures.Regarding frictional wear performance,between 400℃and 800℃,the cladding layer exhibits an average friction coefficient of 0.4,with the primary wear mechanisms being abrasive wear,adhesive wear,and a minor degree of plastic deformation.

Surface hardening of Fe-based alloy powders by Nd:YAG laser cladding followed by electrospark deposition with WC-Co cemented carbide

This paper presents the results of a study concerned with the surface hardening of Fe-based alloys and WC-8Co cemented carbide by inte- grating laser cladding and the electrospark deposition processes. Specimens of low carbon steel were processed firstly by laser cladding with Fe-based alloy powders and then by electrospark deposition with WC-SCo cemented carbide. It is shown that, for these two treatments, the electrospark coating possesses finer microstructure than the laser coating, and the thickness and surface hardness of the electrospark coating can be substantially increased.

Laser cladding in-situ carbide particle reinforced Fe-based composite coatings with rare earth oxide addition

Particulate reinforced metal matrix composite(PR-MMC) has excellent properties such as good wear resistance,corrosion resistance and high temperature properties.Laser cladding is usually used to form PR-MMC on metal surface with various volume fractions of ceramic particles.Recent literatures showed that laser melting of powder mixture containing carbon and carbide-forming elements,was favorable for the formation of in-situ synthesized carbide particles.In this paper,rare earth oxide(RE2O3) was added into t...

Microstructure and mechanical properties of Ni-based composite coatings reinforced by in situ synthesized TiB_2 + TiC by laser cladding

A Ni-based composite coating reinforced by in situ synthesized TiB2 and TiC particles was fabricated on Ti6A14V by laser cladding. An attempt was made to correlate the thermodynamic predictions and experimental observation. The micro- structure and the microhardness profile across the coating were investigated by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and a hardness tester. It is found that the coating mainly consists of a large number of reinforcements （black blocky TiB2, flower-like or equiaxial TiC, and fine acicular CrB） and the 7 matrix. The hardness of TiB2, TiC, and CrB reinforcements is much higher than that of the 7 matrix. The dispersive distribu- tion of such high hardness reinforcements causes the increase in hardness of the whole coating. The average value of the hard- ness is approximately Hv0.2 700 in the coating. The hardness of the coating is obviously higher than that of the substrate due to the dispersion strengthening of reinforcements.

Microstructural characterization of titanium matrix composite coatings reinforced by in situ synthesized TiB + TiC fabricated on Ti6Al4V by laser cladding

Titanium-based composite coatings reinforced by in situ synthesized TiB and TiC particles between titanium and B4C were successfully fabricated on Ti6Al4V by laser cladding. Phase constituents of the coatings were predicted by thermodynamic calculations in the Ti-BnC-Al and Ti-B-C-Al systems, respectively, and were validated well by X-ray diffraction （XRD） analysis results. Microstructural and metallographic analyses were made by scanning electron microscopy （SEM） and electron probe micro-analysis （EPMA）. The results show that the coatings are mainly composed of α-Ti cellular dendrites and the eutecticum in which a large number of needle-shaped TiB and a few equiaxial TiC particles are embedded. C is enriched in α-Ti cellular dendrites and far exceeds the theoretical maximum dissolubility, owing to the extension of saturation during laser cladding. The coatings have a good metallurgical bond with the substrate due to the existence of the dilution zone, in which a great amount of lamella β-Ti grains consisting of a thin needle-shaped martensitic microstructure are present and grow parallel to the heat flux direction; a few TiB and TiC reinforcements are observed at the boundaries of initial β-Ti grains.

Effect of Y_2O_3 Content on Microstructure of Gradient Bioceramic Composite Coating Produced by Wide-Band Laser Cladding

To eliminate thermal stress and cracks in the process of laser cladding, a kind of bioceramic coating with gradient compositional design was prepared on the surface of Ti alloy by using wide-band laser cladding. And effect of Y2O3 content on gradient bioceramic composite coating was studied. The experimental results indicate that adding rare earth can refine grain. Different rare earth contents affect formation of HA and β-TCP in bioceramic coating. When the content of rare earth ranges from 0.4% to 0.6%, the active extent of rare earth in synthesizing HA and β-TCP is the best, which indicates that “monosodium glutamate” effect of rare earth plays a dominant role. However, when rare earth content is up to 0.8%, the amount of synthesizing HA and β-TCP in coating conversely goes down, which demonstrates that rare earth gradually losts its catalysis in manufacturing HA and β-TCP.

Microstructure and formation mechanism of titanium matrix composites coating on Ti-6Al-4V by laser cladding

Laser cladding experiments were done on a 5-kW continuous wave CO2 laser to synthesize TiC and TiB rein- fowed titanium matrix composite coatings on Ti-6AI-4V alloy with a mixture of Ti and B4C precursor powder. The ther- modynamics of the reactions were calculated and analyzed. The microstructure and phase evolution of TiB and TiC com- posites were investigated. The results showed that the chemical reaction between Ti and B4C would release much heat, and these compounds, TiC, TiB, and small amount of TiB2, can be formed on the surface of Ti-6AI-4V alloy if the supplied en- ergy is sufficient to excite the reaction among the initial products. A good metallurgical bond between the coating and the substrate can be achieved. The microhardness of coating was irregular and the maximum value was approximately HV600.

Microstructural evolution of titanium matrix composite coatings reinforced by in situ synthesized TiB and TiC by laser cladding

Titanium-based composite coatings reinforced by in situ synthesized TiB and TiC particles were successfully fabricated on Ti6Al4V by laser cladding using Ti-B_4C-Al or Ti-B_4C-C-Al powders as the precursor materials.The microstructural and metallographic analyses were made by X-ray diffraction（XRD）,optical microscope（OM）,scanning electron microscopy（SEM）,and electron probe microanalysis （EPMA）.The results show that the coatings are mainly composed ofα-Ti cellular dendrites and a eutectic transformation product in which a large number of coarse and fine needle-shaped TiB and a few equiaxial TiC particles are homogeneously embedded.A thin dilution zone with a thickness of about 100μm is present at the interface,and it consists of a few TiB and TiC reinforcements and a large number of lamella grains growing parallel to the heat flux direction in which a thin needle-shaped microstructure exists due to the martensitic transformation. The microstructural evolution can be divided into four stages：precipitation and growth of primaryβ-Ti phase,formation of the binary eutecticumβ-Ti＋TiB,formation of the ternary eutecticumβ-Ti＋TiB＋TiC,and solid transformation fromβ-Ti toα-Ti.

In-situ TiC Reinforced Composite Coating Produced by Powder Feeding Laser Cladding

A Ni-base alloy composite coating reinforced with TiC particles of various shapes and sizes on medium carbon steel substrate was produced by multilayer laser cladding. The chemical compositions, microstructures and surface morphology of the cladded layer were analyzed using energy dispersive X-ray spectroscopy （EDX）, scanning electron microscope （SEM）, and X-ray diffractometry （XRD）. The experimental results showed that an excellent metallurgical bonding between the coating and the substrate was obtained. The microstructure of the coating was mainly composed of γ-Ni dendrites, a small amount of CrB, Ni3B, M23C6 and dispersed TiC particles. Much more and larger TiC particles formed in the overlapping zone, which led to a slightly higher microhardness of this zone. The maximum microhardness of the coating was about HV0.21200. The effects of the laser processing parameters on the microstructures and properties of coating were also investigated.

Microstructure and Thermal Physical Parameters of Ni60-Cr_3C_2 Composite Coating by Laser Cladding

To satisfy performance and long life requirements for hot forging die,Ni60-Cr3C2 composite coatings were prepared on the high-speed steel W6Mo5Cr4V2 using laser cladding technology.Laser clad coatings with different ratios of Ni60：Cr3C2 were investigated by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,energy-dispersive X-ray analysis（EDX） and micro-hardness tester,respectively.Specific heat capacity and thermal conductivity were measured by Laser Thermal Constant Meter.Thermal expansion coefficient and elastic modulus were measured by Dynamic Mechanical Thermal Analyzer and Electro-Hydraulic Servocontrolled Testing System,respectively.The results indicated that Ni60＋50wt% Cr3C2 composite coating had dense and homogeneous structure,as well as a metallurgical bonding with the substrate.With the increase of Cr3C2 content,volume of chromium-containing compounds in the composite coating increased,microhardness increased and microstructure refined.The thermal physical parameters results showed that Ni60＋50wt% Cr3C2 composite coating was overall worse than W6Mo5Cr4V2,but had a higher hot yield strength to alleviate hot fatigue and surface hot wear of hot forging die during hot forging and thus improve the service life of hot forging die.

Microstructure of Cu-based Amorphous Composite Coatings on AZ91D Magnesium Alloy by Laser Cladding

To improve the sliding wear resistance of AZ91D magnesium alloy, Cu-based amorphous composite coatings made of CuaTTi34Zr11Nis and Cu47Ti34Zr11Ni8＋20 wt pct SiC powders were fabricated on AZ91D magnesium alloy by laser cladding, respectively. SEM （scanning electron microscopy）, EDS （energy dispersive X-ray spectroscopy）, XRD （X-ray diffraction） and TEM （transmission electron microscopy） techniques were employed to study the phases of the coatings. The results show that the coatings mainly consist of amorphous phase and different intermetallic compounds. The reason of formation of amorphous phase and the function of SiC particles were explained in details.

Laser cladding of Ni-based alloy on copper substrate

The laser cladding of Ni1015 alloy on Cu substrate was prepared by a high power continuous wave CO2 laser. Its microstructure was analyzed by optical microscope （OM）, scanning electron microscope （SEM）, and X-Ray diffraction （XRD）. The average microhardness of the cladding coating was Hv 280, which was almost three times of that of the Cu substrate （Hv 85）. OM and SEM observations showed that the obtained coating had a smooth and uniform surface, as well as a metallurgical combination with the Cu substrate without cracks and pores at the interface. With the addition of copper into the nickel-based alloy, the differences of thermal expansion coefficient and melting point between the interlayer and cladding were reduced, which resulted in low stresses during rapid cooling. Moreover, large amount of （Cu, Ni） solid solution formed a metallurgical bonding between the cladding coating and the substrate, which also relaxed the stresses, leading to the reduction of interfacial cracks and pores after laser cladding.

Superior corrosion resistance-dependent laser energy density in(CoCrFeNi)95Nb5 high entropy alloy coating fabricated by laser cladding

(CoCrFeNi)95Nb5 high entropy alloy(HEA)coatings were successfully fabricated on a substrate of Q235 steel by laser cladding technology.These(CoCrFeNi)95Nb5 HEA coatings possess excellent properties,particularly corrosion resistance,which is clearly superior to that of some typical bulk HEA and common engineering alloys.In order to obtain appropriate laser cladding preparation process parameters,the effects of laser energy density on the microstructure,microhardness,and corrosion resistance of(CoCrFeNi)95Nb5 HEA coating were closely studied.Results showed that as the laser energy density increases,precipitation of the Laves phase in(CoCrFeNi)95Nb5 HEA coating gradually decreases,and diffusion of the Fe element in the substrate intensifies,affecting the integrity of the(CoCrFeNi)95Nb5 HEA.This decreases the microhardness of(CoCrFeNi)95Nb5 HEA coatings.Moreover,the relative content of Cr2O3,Cr(OH)3,and Nb2O5 in the surface passive film of the coating decreases with increasing energy density,causing corrosion resistance to decrease.This study demonstrates the controllability of a high-performance HEA coating using laser cladding technology,which has significance for the laser cladding preparation of other CoCrFeNi-system HEA coatings.

Research progress of laser cladding self-fluxing alloy coatings on titanium alloys

Laser cladding is a new surface modification technology, and is widely used for fabricating wear and corrosion resistant composites coatings. Self-fluxing alloys have many advantages, such as excellent properties of deoxidizing and slagging, high wear resistance, low melting point and easy cladding, and are often used in laser cladding to improve wear and corrosion resistance of titanium and its alloys. In this paper, the recent development of Ni-based and Co-based self-fluxing alloy coatings which includes the influenee of rare earth and ceramic particles in coatings are summarized. Besides, the effects of processing parameters, such as laser power and scanning speed, on coatings are reviewed. Finally, the trend of development in the future is forecasted.

Influence of cross correlation step length on the surface stress of thin laser cladding Fe314 alloy coatings

To measure the surface stress of thin laser cladding coatings with Rayleigh waves based on the cross correlation function, this pa- per introduced the influence of cross correlation step length on the stress measurement. Flat-shaped specimens made of laser cladding Fe314 alloy coatings were performed by static tensile tests, and Rayleigh wave signals were collected during the test process with an ultrasonic pulser and receiver instrument combined with two Rayleigh wave transducers. The difference in time of flight between two signals was de- termined based on the cross correlation function. The microstructure was observed by scanning electronic microscopy. The influence of the stress on the propagation velocity of Rayleigh waves and the relationship between the difference in time of flight and tensile stress under dif- ferent cross correlation step lengths were analyzed. The inhomogeneous deformation of the coatings affects the relationship between the dif- ference in time of flight and tensile stress; the stress measurement of the coatings is nearly constant with the increase of cross correlation step length when it attains one cycle.

A COMPREHENSIVE MODEL OF LASER CLADDING BY POWDER FEEDING

A novel model was presented to predict the evolutionary development of cladding layer, and a method based on Lambert-Beer theorem and Mie's theory was adopted to treat the interaction between powder stream and laser beam. By using the continuum model and enthalpy-porosity method, the fluid flow and heat transfer in solid-liquid phase change system were simulated. The commercial software PHOENICS, to which several modules were appended, was used to accomplish the simulation. Numerical computation was performed for Stellite 6 cladding on steel, the obtained results are coincident with those measured in experiment basically.

Characterization of Fe_3Si-based coatings on low silicon steel by pulsed Nd:YAG laser cladding

The Fe3Si based coating was produced on the Fe-1 Si steel surface by a pulsed Nd：YAG （yttrium aluminum garnet） laser. Its phase constitution and microstructure were characterized by using X-ray diffraction （XRD）, optical microscope （OM）, and field emission scanning electron microscope （FESEM） with associated energy dispersive spectroscopy （EDS） and transmission electron microscopy （TEM）. The hyperfine structure of the coating was studied by Mrssbauer spectra （MS） and the magnetic property was also measured at room temperature by a vibrating sample magnetometer （VSM）. The obtained coating is pore and crack-free with dense microstructure and high Si content. The metallurgical bonding between the coating and the substrate was realized. The microstructure of the coating is typical fine dendrites. The major phase was confirmed by XRD and TEM to be the ordering D03 structured Fe3Si phase. In addition, there were smaller amounts of the Fe5Si3 phase and the γ-Fe phase in the coating. Compared with the substrate, the laser cladding coating has a lower saturation magnetization and a higher coercive force. The poor magnetic property might be because of rapid solidification microstructure and phase constitution in the coating.

Effects of Powder Feeding Rate on Interaction between Laser Beam and Powder Streamin Laser Cladding Process

A theoretical model was presented to calculate the laser intensity distribution and the particle temperatures at different sites of the workpiece in the laser cladding process. By using this model, the effects of the powder feeding rate on the laser intensity distribution and the particle temperatures were investigated, the calculated results under the condition of different injection angles were also plotted. It is shown that with increasing the injection angle, the laser intensity distributions are similar but the peak value of the laser intensity decreases. Simultaneously, the peak value of the particle temperature increases and the distribution of the particle temperatures gets central symmetrical gradually. These tests results should be considered in model of laser cladding due to their subtle effects on the dynamic processes in laser molten pool.

Effect of coaxial laser cladding parameters on bead formation

We investigated the shape and morphology of nickel-based powder particles (Sulzer Metco) and coatings produced by laser gas-powder deposition onto steel substrates. Laser deposition was performed using an LC-10 IPG-Photonics laser complex equipped with a 10-kW fiber laser. The shape and microstructure of the samples were studied using optical and electronic microscopy and X-ray diffraction analysis. The results showed that the deposition speed and laser power significantly influenced the shape and size of the beads. The depth of diffusion of nickel into the steel substrate after deposition was less than 20 μm; the microstructure of the resulting coating was fcc Fe3Ni. As a result, detailed information about the form and shape of the filler powder, modes of its deposition, and the resulting coating structure was obtained; this information is important for the production of high-quality products by additive technologies.